1. Field of the Invention
The present invention relates to a flexible disk apparatus. More particularly, it relates to a magnetic head positioning device in the flexible disk apparatus to save energy in stand-by condition of the apparatus.
2. Discussion of Background
FIG. 1 is a diagram showing an essential part of the head position determining device of a conventional flexible disk apparatus. In FIG. 1, a reference numeral 1 designates a flexible disk as a storage medium having coaxially formed data tracks for recording and reproducing data. The flexible disk held in a jacket 2 is attachable to and detachable from the flexible disk apparatus. A spindle motor 3 is provided to rotate the flexible disk 1 supported by a hub 4. A carriage 5 having a magnetic head 6 at its one end is driven by a step motor 7 through a metallic belt 8 to be moved in the radial direction of the flexible disk 1 by the aid of guiding rods 9 so that the magnetic head 6 is brought to a predetermined position in the data tracks of the flexible disk 1. A reference numeral 11 designates a track 00 sensor which detects a condition that the magnetic head 6 is at a home position in the outermost circumference of the tracks in the flexible disk 1, i.e. at a track 00 position. The track 00 sensor is constituted by a light-emitting diode 11a as a light-emitting element and a semiconductor photosensor 11b as a light-sensitive element which are adapted to face each other through the light-shielding plate when the magnetic head is brought to the track 00 position. An electric circuit 12 includes a position-judging means for judging the positon of the head 6 depending on a signal A from the track 00 sensor 11 and a step-motor excitation-pulses B applied to the step motor 7 and is connected to the above-mentioned elements.
FIG. 2 shows connection between the electric circuit 12 and the magnetic head 6, the sensor 11 and other elements. The electric circuit 12 includes an index-detection circuit 12a, a revolution-detection circuit 12b, a head-load actuating circuit 12c, an erasure actuating circuit 12d, a recording-reproducing circuit 12e, a head 0/1 selection circuit 12f, a recording-enable-notch detecting circuit 12g, a track 00 detection circuit 12h, a track counter 12i, an indicator driving circuit 12j, a step motor driving circuit 12k, a device number selection circuit 121, a DC motor driving circuit 12m and so on. In FIG. 2, a numeral 121 designates a signal connector, a numeral 122 a revolution index detector, a numeral 123 a head-load solenoid, a numeral 124 a recording-enable-notch detector, a numeral 125 a panel indicator and a numeral 126 a revolution speed detector.
FIGS. 3a and 3b conventional circuits of the track 00 sensor 11 and a position-judging means of the electric cirucit 12.
In FIG. 3a, the light-emitting diode 11a is disposed facing the semiconductor photosensor 11b, each of which is connected to a power source through a resistor Rd or a resistor Rs. The cathode side of the diode or the photosensor is grounded. In this case, the light-emitting diode 11a is lit. If the light-shielding plate is not interposed between the semiconductor devices, the semiconductor photosensor 11b is turned on, whereby potential at the anode side becomes an earth level to generate an L level signal A. This fact represents that the magnetic head 6 is not at the track 00 position.
On the other hand, when the light-shielding plate 10 is between the light-emitting diode 11a and the semiconductor photosensor 11b to interrupt light, the semiconductor photosensor 11b is turned off to thereby generate an H level signal A from the anode side. This fact indicates that the carriage 5 is brought to the home position and the head 6 is at a position near the track 00 position of the substantially outermost circumference of the tracks. However, the distance between the adjacent tracks of the flexible disk 1 is extremely small as about 0.26 mm in the case of 5.25 inches, 96 tracks/inch type flexible disk and about 0.19 mm in the case of 3.5 inches, 135 tracks/inch type flexible disk. Accordingly, it is difficult to discriminate in high accuracy each track depending on the signal A from the semi-conductor photosensor 11b. In the conventional apparatus, therefore, judgement of the head 6 at the track 00 position is made when there is coincidence of the signal A of the semiconductor photosensor 11b and an excitation phase as a specified phase, e.g. PHASE 0 of the step-motor excitation-pulses B applied to the step motor 7. In FIG. 3a, there is provided an AND circuit 13 as the position-judging means for judging the position of the head 6. When the head 6 is brought to the track 00 position, a track 00 signal C is generated from the output side of the AND circuit. The excitation phase of the step motor 7 generally assumes the same phase position at every four steps, namely, each time the head 6 moves four tracks, and the head is stepwisely forwarded in the same direction repeatedly in a manner of PHASE 0, 1, 2, 3, 0, 1, 2, 3, 0. Accordingly, when the signal A of the semiconductor photosensor 11b is generated, judgement is made as to the head 6 being moved near the track 00 position, and the track 00 signal C having an H level is obtainable by detecting through the AND circuit 13 coincidence of the signal A and the excitation phase (PHASE 0) of the step motor 7, whereby the position of the head 6 at the track 00 can be correctly indicated.
FIG. 3b is a circuit diagram showing another conventional device. In the conventional device, in order to increase sensitivity of detection of the movement of the light-shielding plate 10 attached to the carriage 5, a resistor Rs is inserted between the semiconductor photosensor 11b and earth to take out the signal A from the cathode side and the signal A is input into the AND circuit 13 through an inversion and amplification circuit 14.
There have been known to use one or more than two flexible disk apparatuses of this kind as external memory devices of a small capacity computer. In this case, if a power source is disconnected from the spindle motor 3, the step motor 7 and elements in the electric circuit 12 which are not used in the stand-by condition of the apparatus, power is saved in the entire system. Particularly, the saving of power is an essential problem in a portable type computer to be operated by batteries. However, when a power source is disconnected in the conventional device to perform saving of power, a problem arises on the light-emitting diode 11a although there is no problem concerning the spindle motor 3, the step motor 7 and so on. Namely, when the power source for the light-emitting diode 11a is disconnected, there takes place the same effect as interruption of light by the light-shielding plate 10, whereby the track 00 signal C of the AND circuit 13 becomes an H level at the excitation phase (PHASE 0) at every four tracks in the step-motor excitation-pulses B. This causes misleading indication that the head 6 is at the track 00 position.
On the other hand, the flexible disk apparatus is provided with a track counter (not shown) for the purpose of changing recording current and other purposes. The track counter is reset when the track 00 signal C having the H level is detected, and thereafter, the track counter counts seek-step input pulses in the inner or outer radial direction of the flexible disk 1 to know the present position of the head 6. Accordingly, when a misled track 00 signal C is generated, the track counter is reset during counting operation. As a result, the data of the track counter becomes incorrect and the normal operation of the apparatus can not be expected. Further, if a misleading signal on the track 00 position leaks during receiving of a device selection signal, there may takes place error in the computer.
Thus, the conventional apparatus is hindered to disconnect the light-emitting diode 11a from the power source as the spindle motor 3 and step motor 7, with the result of difficulty in saving energy during stand-by condition of the apparatus. A current to be passed in the light-emitting diode 11a is 20 mA or so, which is not negligible as a power produced during the stand-by condition of the apparatus because current to be passed to other logical circuits such as CMOS circuit, CMOS-LSI etc. can be extremely small.